1. Field of the Invention
The present invention is generally related to a backlight unit in a liquid crystal display (LCD), and more particularly to a backlight unit having a reflecting device for enhancing light directivity.
2. Description of the Prior Art
Light emitting diodes (LEDs) have the characteristics of low power consumption, high efficiency, long lifetime, etc., as well as mercury-free environmental advantage. Besides, as LEDs are applied as a backlight source for various flat panel displays, excellent color representation can be obtained. Thus, the application of LEDs in displays has drawn great attention in the recent years.
A backlight unit can be categorized into edge type and direct type, based on the position of the light source. In the past, LCDs are predominantly applied in notebook computers and monitors and thus the backlight units thereof require only light weight, compact size, and thin thickness. Thus, an edge type backlight unit can satisfy such requirements. However, as the development of a super-large-sized backlight unit for a LCD television is proceeding, the considered constituents include sufficient image brightness, a wide viewing angle, high contrast, and long usage lifetime. Therefore, the direct type backlight unit becomes the main stream in the application for large-size LCDs.
In a traditional direct type LED backlight unit, the upright plate 140 is provided to surround the LED light source module, as shown in FIG. 1A (three-dimensional view) and FIG. 1B (side view). The upright plate 140 is to block and reflect the light emitted from the LED light source 122 (either Lambertian or side-emitting type LED) to the upright plate 140. The upright plate 140 is not designed to have additional reflecting structures or light-directing structures. Thus, on top of the upright plate 140, optical components, such as diffuser sheet, diffuser plane, or brightness enhancement film (BEF), are provided. The optical performance of the backlight unit can be improved by diffusing light and controlling light directivity via various optical components.
The upright plate 140 is used to simply reflect light without the functionality of controlling light directivity. Besides, the light reflected by the upright plate 140 is not evenly distributed. The optical performance of the backlight unit cannot be improved without light diffusing optical components, such as diffuser sheet or diffuser plane, to evenly distribute light and without light-directing component, such as brightness enhancement film, to control light directivity. The use of various optical components is unavoidable in order to control the light directivity and enhance the brightness of the backlight unit. However, the above mentioned optical components take space in a backlight unit and it becomes obstruction in thinning a LCD. Besides, the use of optical components increases production cost.
To solve the above-mentioned problems, a new structure for a backlight unit is still needed to achieve the target of thinning a LCD and to improve light directivity, enhance brightness, and lower production cost, in order to fulfill market need.